Not Applicable.
Not Applicable.
This invention relates to an optical image separator, a strain analysis device and to reflection polariscopes for the stress analysis of a component. Typical uses are in the aeronautical, automobile or glass industries to facilitate stress analysis of real components. Applicability includes crack detection and analysis; residual stress evaluation; operation in static, cyclic and dynamic events and provision of full-field principal strain data.
In Journal of Strain Analysis, 33(1): 1-16, 1998, is an Article by E. A. Patterson, and Z. F. Wang entitled xe2x80x9cSimultaneous observation of phase-stepped images for automated photoelasticityxe2x80x9d. In U.S. Pat. No. 5,978,087 Nov. 2, 1999 a technique for simultaneous capture of phase-stepped images is described using beam-splitting devices. Also in the Proceedings of the International Conference on Photoelasticity: New Instrumentation and Data Processing Techniques, published by SIRA, London, (1): 1-6 is an Article by S. J. Haake and E. A. Patterson entitled xe2x80x9cPhotoelastic analysis using a full-field spectral contents analyserxe2x80x9d wherein is described a technique for sequential capture of images for the purpose of spectral contents analysis.
U.S. Pat. No. 6,055,053 entitled Full Field Photoelastic Stress Analysis, which is incorporated herein by reference, discloses an apparatus for producing four images of an object undergoing stress; however, because the images are not brought to a single plane four cameras are required to obtain the images required to perform stress analysis.
An optical assembly divides a single image into a plurality of images which are simultaneously projected onto a single sensor array. The optical assembly is arranged so that each of the plurality of images can be made to pass through a filter of a different type. For example, a polarizing filter of a different orientation, or a filter which passes a different spectral band. In this way a single digital camera having a single chip sensor array can simultaneously receive multiple substantially identical images which have been acted on by different filters. This allows data capture from a single frame of a single camera to be used to perform stress analysis, or spectral analysis. This is particularly useful when high speed image capture is desired which contains stress or spectral data, because each frame captured from the sensor array contains multiple images which can be processed to obtain stress or spectral data.
According to the first aspect of the present invention there is provided an optical image separator comprising:
1. an objective lens partitioned into n parts, where n is an integer greater than one, such that the objective lens is capable of reproducing n output beams from one input beam;
2. an optical element placed either before or after the objective lens and partitioned into n parts for each said output beam such that each part has a different effect on the state of polarization; and
3. a recording device for the simultaneous capture of the n images formed by the n output beams.
According to the second aspect of the device, the beam splitting can be achieved by the insertion of n wedges in the light path adjacent to the objective lens, which need not then be partitioned.
According to the third aspect of the invention, the optical element introduces equal changes of polarization into the n images and a bandwidth filter is provided for each image where the central wavelength of each filter are all different so that full-field spectral contents analysis can be performed using the resultant images.
According to the fourth aspect of the invention, there is provided a polarimetric device for stress or chemical analysis comprising an optical image separator as defined above and a source of polarized light.
According to the fifth aspect of the invention there is provided a reflection polariscope comprising an optical image separator as defined above and a source of polarized light.
According to the sixth aspect of the invention a polarized white light is used, with the bandwidth filter removed and the recording device is capable of recording color images.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.